Any decisions on the three caps i mentioned earlier, can changing them be of any benefit? They are the cheap capxcon caps, i have swapped them out for panasonic fm, except for the 150uf cap in the corner it seems to be of good quality, do you know what this cap does.
So, i was removing the stock op amp and accidentally lifted the solder pad, it is maked as number 5 offset compensation. Can i run a jumper cable. I don't have the circuit diagram. Any advice please.
Thank you !
Thank you !
As others have indicated, 47uF should be the bootstrap, 100uF should be part of the DC feedback loop, and the 220/150uF low voltage is probably the current source decoupling capacitor, C5 as shown here, the original is 100uF:
What does (did) it connect to? As far as I can see, none of the versions had anything connect to pin5:
Should i just leave pin 5 unsoldered in the through-hole. ejp has given a thumbs up, is this the same ejp that designed these boards
Thanks.
Pin 5 on the LM301 and TL071 is for offset null adjustment. The Quad never used that option so yes, leave it dangling.
Do you think i will be a good idea to solder a 1000uf cap across the V+ and V- pins. I'm looking around in my spare parts box and the only single channel op-amps i can find are sparkos labs discrete which run quite hot in class-A. Good op-amps, 65 quid each, but current hungry, do you think the op-amp may put a strain on the op-amp power supply.
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Definitely not. A much smaller value such as a 2.2uF or 4.7uF could be beneficial in some cases. No need for anything bigger and very large caps could alter the switch on and off characteristic of the amp (causing a thump).
If the discrete amps run hot, they almost certainly pull more current than the resistor/Zener shunt supply can handle. That's easily fixed by altering the resistor, but you need to know the current the opamp draws in order to arrive at a suitable value.
Yep, I would go with that. I would probably (these days) add something like a 1 ohm carbon resistor in series with a film cap while relying on the electrolytics inherent 'lossy' nature. As always, you need to know what you are trying to achieve when it comes to lowering supply impedance at hf.
Thanks!
I was told by another member that uses burson discrete op-amps that discrete op-amps pull more juice from the power supply, so that by soldering a large cap across the op-amp power pins, the large cap can then act like a local power supply for the op-amp to pull on in case there are any issues with thepower supply that feeds the op-amp
But if that is wrong i will bow to your greater wisdom
I was told by another member that uses burson discrete op-amps that discrete op-amps pull more juice from the power supply, so that by soldering a large cap across the op-amp power pins, the large cap can then act like a local power supply for the op-amp to pull on in case there are any issues with thepower supply that feeds the op-amp
But if that is wrong i will bow to your greater wisdom
You would need to know the current draw by measurement to say for sure but given they run 'hot' is definitive proof they draw a lot more current.
In the Quad it is the series feed resistors to the opamp power pins that determine how much current can be drawn. The Zener clamps the voltage to 12 volts.
If you have a 50 volt rail, a 2k7 resistor and a 12 volt Zener you have 14 milliamps available calculated as (50-12)/2700
That 14ma flows 100% in the Zener with no opamp fitted. If the opamp draws 10ma then you have 4ma in the Zener and 10ma in the opamp. If the opamp wants to draw more than 14ma then the supply voltage will fall away as the resistor cannot supply the load.
The cap could at best only deliver a transient current pulse... which opamps don't do anyway, it cannot deliver long term current that cannot be delivered from the resistors.
In the Quad it is the series feed resistors to the opamp power pins that determine how much current can be drawn. The Zener clamps the voltage to 12 volts.
If you have a 50 volt rail, a 2k7 resistor and a 12 volt Zener you have 14 milliamps available calculated as (50-12)/2700
That 14ma flows 100% in the Zener with no opamp fitted. If the opamp draws 10ma then you have 4ma in the Zener and 10ma in the opamp. If the opamp wants to draw more than 14ma then the supply voltage will fall away as the resistor cannot supply the load.
The cap could at best only deliver a transient current pulse... which opamps don't do anyway, it cannot deliver long term current that cannot be delivered from the resistors.
Thanks! Here's the specs for the sparkos op-amp:
140 dB Open Loop Gain
415nV RMS (2.9nV√HZ) Noise to 20KHZ
+/- 18 Vcc Max
15mA Class A Output Current
65mA Max Output Current
14mA Supply Current
< 300µV Typical Offset
Sparkos says : " Every stage in my device operates in class A mode with fairly high bias currents. The OPAs only draw 5mA total per amplifier. This is spread across their input stage, gain stage, and output stage. It leaves their devices somewhat current starved, and their output stage is undoubtedly class B or at best it's biased with only a couple mA. My device's output stage alone is biased at 7.5mA. My input stage and gain stages are biased at 3mA each. In total, my devices run at ~14mA / amplifier while the OPAs run 5ma. High current biasing, especially in the output stage always sound better and make for more linear amplification. Keep in mind, that 14mA biasing current isn't possible in monolithic op amps either due to their power dissipation limitations. This limits the amount of current that IC op amps can use for biasing."
My psu for the ljm quad boards is +/-40 volts. Can i adjust the op-amp power supply to accept the sparkos op-amp?
Thanks!
140 dB Open Loop Gain
415nV RMS (2.9nV√HZ) Noise to 20KHZ
+/- 18 Vcc Max
15mA Class A Output Current
65mA Max Output Current
14mA Supply Current
< 300µV Typical Offset
Sparkos says : " Every stage in my device operates in class A mode with fairly high bias currents. The OPAs only draw 5mA total per amplifier. This is spread across their input stage, gain stage, and output stage. It leaves their devices somewhat current starved, and their output stage is undoubtedly class B or at best it's biased with only a couple mA. My device's output stage alone is biased at 7.5mA. My input stage and gain stages are biased at 3mA each. In total, my devices run at ~14mA / amplifier while the OPAs run 5ma. High current biasing, especially in the output stage always sound better and make for more linear amplification. Keep in mind, that 14mA biasing current isn't possible in monolithic op amps either due to their power dissipation limitations. This limits the amount of current that IC op amps can use for biasing."
My psu for the ljm quad boards is +/-40 volts. Can i adjust the op-amp power supply to accept the sparkos op-amp?
Thanks!
If your opamp is pulling 14 milliamps and if each rail is around 40 volts DC and if the Zener is a 12 volt type then you would need something like a 1.2k 1 watt resistor. That would pass about 23 milliamps allowing a a few milliamps margin and a suitable Zener current.
At 14ma opamp current the Zener would dissipate about 100 mw and the resistor around 650 mw. The opamp isn't called on to deliver anything over a few hundred microamps in a standard 405 so that doesn't really factor in the equations.
At 14ma opamp current the Zener would dissipate about 100 mw and the resistor around 650 mw. The opamp isn't called on to deliver anything over a few hundred microamps in a standard 405 so that doesn't really factor in the equations.
So the whole idea of large caps is wrong do you think it's more the power supply that needs to be addressed, perhaps i was misinformed, because i was thinking of soldering large caps onto the back of the 0.1uf decoupling caps, most forum members are using 100uf -200uf, would going larger than this have any benefits
Not sure, thought a larger cap may give lower esr, higher ripple current rating, it may store more energy if needed in case of a big bass hit, or may act like a local power supply for the boards to pull on and provide better seperation between the channels rather than them interacting with each other.
Thank you.
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Thanks ! Do you know where the 2.7k resistor is, managed to find a quad 405 schematic on line but cannot spot this resistor. If possible can you mark the snapshot below.
